1. Field
This disclosure relates to an apparatus and a method for river water purification using a treatment soil layer and a permeable filtering medium layer, and more particularly, to an apparatus and a method for river water purification using a treatment soil layer and a permeable filtering medium layer capable of increasing a treatment flux of river water regardless of a coefficient of water permeability of soil and effectively removing nitrogen, phosphorus and nutrient salts by stably forming an anaerobic condition.
2. Description of the Related Art
The traditional river improvements based on embankment cause straightening of the river and destruction of the river environment, and due to this, the residence time of a river stream is reduced, resulting in loss of self-purification capacity of the river. Since river contamination is characterized by a large water volume and a low contamination level, application of a wastewater treatment process to the entire water volume of the river is not practical from the economic point of view. Therefore, demand for a nature-friendly water purification technique capable of restoring the self-purification of river and naturally maintaining clean water is increasing.
Water purification techniques using contact oxidation facilities, artificial wetlands, artificial vegetated islands, and the like have advantages of excellent biological removal efficiency due to vegetation and microorganisms and improvement in scenery. However, they also have limitations in that the function cannot be maintained or the structure itself may be collapsed in the event of a flood. In order to overcome these limitations, a nature-friendly water purification method in consideration of basin spaces including surface water, underground water, and land is needed.
In this aspect, in Korean Patent Registration No. 586496 (Underflow type wastewater treatment system constructed at the edge of water and wastewater treatment method of the same), an underflow purification land is formed at the edge of a river or a lake to decompose organic materials using filtration and adsorption by soil and microbial metabolism and to remove nitrogen and phosphorus by planting vegetation, so as to improve water quality. However, in this method, the treatment capacity absolutely depends on the coefficient of permeability of the soil layer. Therefore, in the case where soil with low permeability is used, it is difficult to ensure the treatment capacity, and since clogging occurs during a long-term operation, there is a problem in that it is difficult to maintain the operation.
In order to solve the problems, a multi stage soil layer method has been developed. A multi stage soil layer method disclosed in Japanese Unexamined Patent Publication No. 2004-154696 is based on the purification method using soil, with the structure improved to change a fluid flow. Specifically, in the method, soil is formed into blocks with a predetermined shape, the blocks of the soil layer are laminated in a reactor in the shape of a brick, and a water flow layer is formed between the soil layers to enhance water permeability. In the case of this method, there is an advantage in that the treatment volume is increased by enhancing the water permeability of the soil layers. However, since most of river water permeates through the permeable layer during permeation of the river water, a quantity of water permeating into the soil layer which plays an important role in the treatment of the river water is reduced, and thus there is a problem in that the treatment efficiency is relatively decreased. Particularly, since the velocity of the fluid permeation is relatively high, a residence time of the fluid in the soil layer is reduced. Accordingly, it is very difficult to form an anaerobic condition which is necessary for denitrification playing an important role in nitrogen removal, and thus nitrogen removal efficiency is decreased.